Method for content synchronization when broadcasting data in a wireless network

ABSTRACT

The present disclosure relates to base station and method for content synchronization when broadcasting data in a communications network. The base station comprises a receiver receiving data sequences and a transmitter for transmitting data sequences. Each data sequence has a data size and comprises a sequence number (SN). The base station further comprises a processing circuitry configured to add byte numbered sequence numbers to said data sequences passed between layers in a protocol stack for transmission to a transceiver station.

RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/493,658 filed on Sep. 23, 2014, which is a divisional ofco-pending U.S. patent application Ser. No. 12/513,305, filed May 1,2009, which is a 371 of International Application No. PCT/SE2007/050798,filed Oct. 31, 2007 which claims benefit to Swedish Application No.0602318-8 filed Nov. 1, 2006, the disclosures of which are incorporatedherein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to telecommunications systems in generaland distribution of broadcast/multicast data in cellular systems inparticular.

BACKGROUND

In MBMS architecture, the BM-SC is the Broadcast Multicast ServiceCentre, which is the application level server providing the multimediacontent. This is illustrated generally in FIG. 8.

The MBMS GW is responsible for the user plane processing of the MBMSdata, including such functions as content synchronization and deliveringthe data over a multicast IP transport to the relevant eNodeBs. The MBMSGW also executes control over the start and stop of the services andacts as a mediator between the access agnostic multimedia contentsources and the LTE specific access network.

The MCE (MBMS Control Entity) is a radio resource control entity, whichis responsible mainly for the coordinated allocation of radio resourcesover multiple cells in case of Single Frequency Network (SFN)transmission mode.

To efficiently support the distribution of broadcast/multicast data incellular systems (e.g., the distribution of multimedia content, TVchannels), the concept of Single Frequency Network (SFN) transmission isoften used. This means that the same content is sent from multiple basestations in a time synchronized manner, which allows the receiving userterminal to combine the signals from multiple base stations and therebyachieve a good reception quality also at the cell edge.

In order the SFN concept to work, a mechanism is needed that achievesthe synchronization of both the content, meaning that the same data issent from multiple base stations in the same radio resource block andalso the time synchronization of the base stations, meaning that thetransmission in the identical radio resource blocks at multiple basestations are time aligned accurately enough.

The SFN concept is used, for instance, for the realization of theMultimedia Broadcast Multicast Service (MBMS) in UTRAN and the sameprinciple will be used in the LTE system as well.

In UTRAN the MBMS content synchronization is done by the RNC node aspart of the resource and scheduling control functionality in the MAClayer. However, in order this solution to work it is required to locatethe radio interface scheduling and L2 processing (e.g., segmentation) ina central user plane processing node. In LTE these radio resourcecontrol functions will be located in the eNodeB along with thecorresponding MAC and lower layer protocol layers. Therefore the earliersolutions are not favorable for LTE and they are not directly applicableeither, unless some of the L2 protocol layers (e.g., RLC/MAC) are movedfrom the eNodeB to the central MBMS Gateway (MBMS GW) node or some newprotocol layers with L2 functionality (e.g., segmentation/concatenation)are introduced between the RLC/MAC and upper layers.

Similar solutions are being discussed also for LTE, where the user planeprocessing in the MBMS GW would include RLC/MAC layer or a newlyintroduced protocol layer doing the segmentation/concatenation accordingto the radio resource block size.

These solutions are not desirable in LTE since they would require RANfunctionality in the MBMS GW node, which would add to the complexity ofthe node and would significantly differ from the user plane processingfunctions in the central node used for unicast traffic.

It would be desirable to use a content synchronization method thatallows keeping the user plane processing in the MBMS GW node as simpleas possible and free of any RAN specific processing, i.e., similar tothe user plane processing functionality for unicast traffic.

SUMMARY

The present invention solves the problem of content synchronization bythe use of byte level sequence numbering in the central MBMS GW node.This means that the GW only needs to add byte numbered sequence numbersto the bypassing PDUs, i.e., it can be free of any RAN specific userplane processing. The receiving eNodeBs will be able to unambiguouslymap the received MBMS PDUs to the corresponding radio resource block byrelying on the byte numbering and on the pre-configured radio resourceblock sizes.

Other advantages of the invention according to the described embodimentsinclude:

-   -   A simple user plane processing function in the central GW node        will be achieved by the user plane protocol stack can be        identical to the one used for unicast data.    -   The GW node may be free of any RAN specific user plane        processing (e.g., segmentation/concatenation, knowledge about        radio resource block parameters, etc.)    -   No new protocol layer needs to be defined, the required sequence        numbering can be added to the header of the tunneling protocol        (e.g., into GTP-U).

The problem is solved and the advantages are obtained by means of anarrangement for content synchronization when broadcasting data from aninfrastructure node in a communications network. The arrangementcomprises a receiver receiving data sequences and a transmitter fortransmitting data sequences, wherein each data sequence has a data sizeand comprises a sequence number. The arrangement further comprises aprocessing arrangement configured to add byte numbered sequence numbersto said data sequences passed between layers in a protocol stack fortransmission to a transceiver station.

Preferably, sequence numbers are added into layer of transport networkprotocol. In one embodiment, the sequence number of a subsequent packetis obtained by incrementing a sequent number of previous packet by sizeof a previous packet. The size is expressed in number of bytes of saidsequence. According to one embodiment the sequence numbers are added tothe header of a tunneling protocol, e.g. GPRS Tunneling Protocol-User.The arrangement may support variable Multiple Access Control (MAC)header size. The arrangement may be configured to add a packet levelsequence number to the data sequences together with a byte levelsequence number. In an alternative embodiment the arrangement isconfigured to add a size of a MAC overhead corresponding to said datasequences to a byte sequence number assigned to said data sequence.

In one preferred embodiment data sequences comprising a packet headerand no user data part are transmitted. The transmission is at a fixedoutput rate performing a buffering in said arrangement and sending saiddata sequences when said buffer is becoming empty. The transmission maycarried out by measuring an output rate of the arrangement and based onthat, predicting a buffer occupancy at a receiver node and sending thedata sequences when said receiver buffers are predicted to become empty.

The invention also relates to a base station for content synchronizationwhen broadcasting data in a communications network. The base station inits simplest form comprises a receiver receiving data sequences (PDUs)and a transmitter for transmitting data sequences, wherein each datasequence has a data size and comprises a sequence number. A datasequence comprises added byte numbered sequence numbers to said datasequences passed between layers in a protocol stack and that said basestation comprises a processing arrangement configured to map saidreceived data sequences to a corresponding radio resource block byrelying on a byte numbering and on a pre-configured transport block, TB,sizes. Preferably, the data sequences are multimedia data sequences.According to one embodiment the data sequences may be fixed size orvariable size TBs. The size of said TBs is assumed to be pre-configuredby a Multimedia Broadcast Multicast Service (MBMS) radio resourcecontrol entity before the start of a MBMS service. In one embodiment,the processing arrangement is configured to determine if a PDU is lostand which PDU or which part of a PDU it should resume transmission anddetermine a PDU with partial content. If data sequences lost, theprocessing arrangement may use a sequence number of a subsequentreceived PDU and a sequence number of a last received PDU to determinethe lost number of bytes of data and determine transmission continuationwith subsequent PDU in forgoing TB.

According to one embodiment, a Multiple Access Control (MAC) protocolheader within said TB is variable and the base station receives a datasequence with a packet level sequence number added to said PDUs togetherwith byte level sequence number. In an alternative embodiment, MultipleAccess Control (MAC) protocol header within said TB is variable and itreceives a data sequence with size of a MAC overhead corresponding to aPDU added to the byte sequence number assigned to said PDU.

Preferably, the base station may comprise a buffer configured to receivedata sequences comprising a packet header and no user data part, saidpacket header further including a byte level sequence number, which isset according to a virtual data associated with said data sequence.Thus, the processing arrangement is configured to transmit a packet, P,with byte count b(P) at a time where an internal byte count isB(t)=b(P), where t is a current time maintain relating to an internalbyte sequence number that counts transport block containers havingelapsed up said current time (t), B(t) is an elapsed transport blockcontainers up to time t.

Most preferably, the transport blocks are configured by a centralcontrol entity (MCE) in the network to be used for an MBMS transmissionat each base station and designate an absolute time for transmissionstarted. The configuration may comprise on or several of: transportblock encoding format, time-frequency resources assigned, and recurrencepattern in time.

The invention also relates to a method of content synchronization whenbroadcasting data in a communications network. The method comprisesadding byte numbered sequence numbers to data sequences (PDUs) fortransmission to a transceiver station.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in an exemplary way withreference to non-limiting embodiments illustrated in attached drawings,in which:

FIG. 1 illustrates schematically a MBMS protocol architecture,

FIG. 2 illustrates schematically adding byte level sequence numbers,

FIG. 3 illustrates schematically mapping of the byte numbered PDUs intothe appropriate radio resource blocks at the eNodeB,

FIG. 4 illustrates schematically mapping PDUs into the appropriate radioresource blocks at a eNodeB,

FIG. 5 illustrates schematically fixed vs. variable MAC header size,

FIG. 6 is a schematic block diagram of an arrangement according to thepresent invention,

FIG. 7 is a schematic block diagram of a base station according to thepresent invention, and

FIG. 8 illustrates schematically the LTE MBMS Architecture

DETAILED DESCRIPTION

FIG. 1 illustrates an example overall user-plane architecture of a MBMSprotocol, e.g. for LTE.

In the figure:

110 designates a User Equipment comprising protocol layers MBMS packet111, PDPC 112, RNC 113, MAC 114 and PHY 115.

120 designates a base station, eNodeB, comprising protocol layers RNC123, MAC 124, PHY 125, TNL 126 and Sync 127.

130 designates a Central Gateway Node, comprising protocol layers PDPC132, TNL 136 and SYNC 137.

140 designates eBM-SC comprising protocol layers MBMS packet 141 and TNL146. eBM-SC is the source of the MBMS traffic.

SYNC protocols 27 and 137 (further described below) is the protocol tosynchronize data used to generate a certain radio frame. SYNC protocolbetween the MBMS gateway and the eNBs ensures that the same content issent over-the-air from all the eNBs.

The central Gateway (GW) node 130 (e.g., MBMS GW) includes user planeprocessing functionality also covering the functions needed for contentsynchronization. The SYNC 127/137 protocol layer shown in the figure isa logical layer that implements the required support for contentsynchronization. However, this does not necessarily mean a new protocollayer, the required functions (e.g., sequence numbers) may be added tothe existing layers as well, e.g., into the TNL protocol layer 126, 136,146 or into the PDCP layer 111, 131.

According to this embodiment, the GW 130 adds byte level sequencenumbers to the PDCP 131 PDUs (Protocol data Units). An example is shownin FIG. 2. The SN (Sequence Number) of the next packet is obtained bythe SN of the previous packet incremented by the length of the previouspacket (expressed in number of bytes), i.e.SN_(PDU#n)=SN_(PDU#n−1)+size of PDU#n,where n=1, 2, 3, . . .

The sizes illustrated in the drawing are given as example and do notlimited the invention.

This sequence number can be included as part of the Transport NetworkLayer (TNL). For example, it can be added to the header of the tunnelingprotocol or it could be added to the header of the PDCP protocol.Alternatively, a new protocol layer can be introduced for that purposebetween the eNodeB and the GW. In preferred embodiment, the tunnelingprotocol sequence number, e.g., GTP-U (GPRS Tunneling Protocol—User)protocol sequence number possibly extended in length is used.

As mentioned earlier, at the start of the MBMS service the MBMS resourcecontrol entity (e.g., MBMS Control Server: MCS) configures the radioresources to be used at the eNodeBs for that particular MBMS service andit also specifies an absolute time when the eNodeBs should start thetransmission. The control server also triggers the GW to start sendingMBMS data with the byte sequence number reset to an initial value. Fromthat point on, the synchronization is self-sustained based on the bytelevel sequence number method as described, as long as the buffers at theeNodeBs 120 do not run out of data. However, this may not be possible toguarantee in all cases, as the MBMS data may be bursty, meaning thatthere might be idle gaps between bursts of packets.

The following method is an extension to the basic sequence numberingsolution in order to maintain the synchronization also in cases of idlegaps in the data stream.

In order to be able to keep the synchronization at the eNodeBs it needsto be ensured that the buffer 1204 (FIG. 7) at the eNodeBs do not becomeempty. Therefore, during times of idle gaps in the MBMS data stream, theGW inserts dummy PDUs into the stream to fill the eNodeB buffers withvirtual data. The dummy PDUs contain only a packet header and no userdata part. The packet header of the dummy PDU includes a byte levelsequence number, similarly to normal data PDUs. The byte level sequencenumber is set according to the virtual data associated with the dummyPDU. The dummy PDUs are sent from the GW to the eNodeB. These PDUs aretypically not sent on the radio interface. However, it could be allowedto send the dummy PDU also over the radio interface, e.g., as padding inthe physical transport block. The reason for sending the dummy PDU overthe radio interface could be, for instance, to avoid that the UEinterprets the idle gap as a radio link error.

When the eNodeB receives a dummy PDU, it can handle the packet similarlyto normal data packet, i.e., it can buffer the packet, schedule it fortransmission, etc. The only difference in the handling of these dummypackets compared to normal data packets is that there is no real userdata transmission associated with them on the radio interface. ThesePDUs are used just as virtual data for maintaining the synchronization.The use of dummy PDUs is illustrated in FIG. 3.

FIG. 3 shows also how the eNodeB 120 of FIG. 1 and FIG. 7 canunambiguously map the received PDUs, received by the interface 1201 intocorresponding Transport Block (TB). I

Generally, a transport block is an encoded data block prepared for radiointerface transmission and it is transmitted in a designatedtime-frequency resource.

As shown in the example, there are temporarily no data to send afterPDU#1. Therefore the GW inserts dummy PDUs, each with a virtual size of256 Kbyte as indicated in the SN field of the packet header (it is justan example, it could be any size of virtual data). These PDUs do notcontain a data part, only the header, as also shown in the figure. Whenthe dummy PDUs arrive to the eNodeB, the eNodeB processes them as itwould do for normal data packets, i.e., it keeps track in which radioresource block these packets would have been transmitted, if they hadbeen real data. Thereby the eNodeB can continuously maintain in whichradio resource block the next data should be sent. That is, if a new PDUcomes in, after the end of the idle gap (PDU#2 in the example), eacheNodeB will know unambiguously at which time instant and in which radioresource block the data needs to be sent. The arriving data PDU will besent in continuation of the dummy PDUs, i.e., after the virtual sendingof the dummy PDUs are finished.

There needs to be a procedure in the GW to determine when it should senddummy PDUs, i.e., to determine when the eNodeB buffers are becomingempty. There can be basically two different ways to solve this issue:

-   -   by sending at a fixed output rate from the GW, performing the        buffering in the GW and sending dummy PDUs when the GW buffer is        becoming empty, or    -   by measuring the output rate at the GW and based on that,        predicting the buffer occupancy at the eNodeB and sending dummy        PDUs when the eNodeB buffers are predicted to become empty.

In this case of fixed output rate and buffering at the GW, it will sendthe MBMS data packets at a fixed output rate corresponding to the radiolink rate that has been allocated for the given MBMS service on theradio interface. As a result of the fixed output rate at the GW thereneeds to be buffering done in the GW in order to handle the burstinessof the traffic stream, i.e., to absorb the excess traffic during timesof a packet burst. Note that some buffering needs to be maintained alsoin the eNodeB in order to account for the delay variations on thetransport network links between the GW and the eNodeBs.

When the buffer in the GW is becoming empty the GW simply inserts dummyPDUs into the buffer with a virtual data size determined by the GW.

In the case of measured output rate and no-buffering at the GW, the GWis continuously measuring the current rate at which MBMS data packetsare passing by (after being processed in the GW), i.e., no buffering isdone in the GW. Based on the output rate measured for a certain timewindow, the GW can predict the amount of data in the eNodeB buffers.When the GW anticipates that the eNodeB buffers are becoming empty,i.e., the measured output rate is below the radio link rate for sometime, then it starts inserting dummy PDUs into the stream. The size ofthe virtual data associated with the dummy PDUs is determined by the GW.(Note that the dummy PDUs need to be taken into account when measuringthe output rate at the GW.)

This solution may be extended with an optional reporting mechanism fromthe eNodeB to the GW, where the eNodeB can send a report to the GW whenthe buffer level at the eNodeB falls below a certain threshold. Inresponse to this indication the GW can start inserting dummy PDUs intothe stream as long as the buffer level in the eNodeBs goes above thethreshold (in which case a new indication can be sent to the GW).

Finally, there might still be certain exceptional cases when the eNodeBmight lose the synchronization. To handle such cases the eNodeB can usea reporting mechanism toward the GW and/or toward the MBMS controlserver to indicate the loss of synchronization. (An indication for alost synchronization may be the eNodeB buffer becoming empty or theindication may come from radio interface measurements done either by theeNodeB or by the UE.) In such cases the synchronization can bere-established with a method similar to the one used for initialsynchronization. The MBMS control server can assign a re-start time forthe eNodeBs specified in absolute time and may also reset the sequencenumber at the GW. The required signalling communication forre-establishing the synchronization may involve the MBMS control server,the eNodeBs and the GW, where either the control server or the GW may bethe master node coordinating the process. The detailed signallingprocedure can be drawn accordingly.

In order to map the PDUs into the correct transport blocks the eNodeBcan maintain an internal byte sequence number that counts the transportblock containers (in bytes) that have elapsed up to the current time t(measured from a designated start time T0). Let us denote the elapsedtransport block containers up to time t by B(t). Then the eNodeB shouldtransmit the packet P with byte count b(P) at exactly the time where theeNodeB internal byte count B(t)=b(P).

Before the transmission of broadcast services can be started, thecentral control entity (MCE) in the network has to configure thetransport blocks (i.e., their encoding format, the time-frequencyresources assigned to them, including the recurrence pattern in time,etc.) to be used for MBMS transmission at each eNodeB and shoulddesignate an absolute time when the transmission should be started(i.e., designate T0).

FIG. 4 shows how the eNodeB may map the PDUs into the appropriate TBs incase some of the PDUs get lost (crossed over) on the transport network.

For example, if PDU#3 is lost on the transport network, it means thatthe sequence number of the lost PDU is unknown as well. In this case theeNodeB may determine which PDU or which part of a PDU it should resumetransmission in TB#3. Whether TB#2 can be sent out by the eNodeB withpartial content only, i.e., with parts of the TB filled up with padding,depends on the L1 interface details and it is out of the scope of thecontent synchronization scheme.

The eNodeB may use the sequence number of the next received PDU (i.e.,PDU#4) and the sequence number of the last received PDU (i.e., PDU#2) todetermine how many bytes of data is missing and determine where itshould continue with PDU#4 in TB#3.

The above sequence numbering scheme may slightly differ depending on howthe multiplexing of upper layer PDUs into TBs are done in the eNodeB. Itis possible to differentiate basically two main alternatives dependingon whether the MAC protocol header within the TB is fixed or has dynamicsize. For instance, the size of the MAC header could depend on thenumber of PDUs multiplexed into that particular TB. The differencebetween fixed and variable MAC header size cases are illustrated in FIG.5, in which the upper sequence (I) illustrates fixed size and lower (II)sequence variable size.

Thus, fixed MAC header size per TB means that the number of user bitsthat can be carried in one TB is fixed.

Variable MAC header size per TB means the size of the MAC header variesdepending on the numbered of multiplexed PDUs, and the number ofinformation bits that can be carried in a TB depends on the number ofPDUs that have been multiplexed into the TB. This could mean forinstance, that there is a fixed size MAC header part added to eachmultiplexed PDU.

In the basic solution, it is assumed fixed MAC header size, i.e., fixednumber of user bits per TB and the simple byte sequence numberingsolution for content synchronization is sufficient.

In cases of variable MAC header size, the pure byte sequence numberingmay not be sufficient in all cases, especially in case when a number ofconsecutive PDUs get lost on the transport network. In this case, it isnot enough to know only how many information bytes were lost in orderthe eNodeB can catch up with correct synchronization, the eNodeB shouldalso know how many PDUs have been lost.

In order to support the variable MAC header size cases, two possiblesolutions may be used:

-   -   The GW node adds a packet level sequence number to the PDUs        beside the byte level sequence number.    -   The GW adds the size of the MAC overhead corresponding to the        PDU to the byte sequence number assigned to that PDU.

The invention may be implemented in the GW using an arrangement 1301 asillustrated schematically in FIG. 7. The arrangement comprises areceiver 1302, which receives PDUs and a transmitter 1303, whichtransmits PDUs. A processor 1303 handles the adding of byte numberedsequence numbers to the PDUs passed between layers in the protocol stackfor transmission to the eNodeB. The arrangement may further comprise amemory 1305 for storing data and instructions. Clearly, this arrangementcan be implanted using the logical units of the GW.

The invention is not limited to the mentioned examples, standards andtechnical terms. Thus, the invention may be generalized by a gatewaynode, which comprises processing means for content synchronization. Theprocessing means is arranged to operatively use byte level sequencenumbering, whereby the processing means is arranged to add byte numberedsequence numbers to bypassing data sequences passed between the layersin a protocol stack to be send to a transceiver station.

ABBREVIATIONS

SFN Single Frequency Network

MBMS Multimedia Broadcast Multicast Service

LTE Long Term Evolution

RNC Radio Network Controller

MAC Multiple Access Control

RAN Radio Access Network

PDU Protocol data Units

TNL Transport Network Layer

PDPC Packet Data Convergence Protocol,

SN Serial Number

GTP-U GPRS Tunneling Protocol—User

TB Transport Block

RLC Radio Link Control

The invention claimed is:
 1. A base station configured to synchronizecontent when broadcasting data in a communications network, the basestation comprising: a receiver configured to receive data sequences(PDUs); wherein each received data sequence comprises byte-numberedsequence numbers; the base station further comprising: a transmitterconfigured to transmit content of the received data sequence; andprocessing circuitry configured to synchronize transmission with anotherbase station of the content using said byte-numbered sequence numbers,wherein said processing circuitry is configured to determine if a PDU islost.
 2. The base station of claim 1, wherein the same content is sentfrom the base station and the another base station in a same radioresource block.
 3. The base station of claim 1, wherein said processingcircuitry is configured to determine which PDU or which part of a PDUshould be used to resume transmission.
 4. The base station of claim 1,wherein said processing circuitry is configured to use a sequence numberof a subsequent received PDU and a sequence number of a last receivedPDU to determine the lost number of bytes of data and determine atransmission continuation with a subsequent PDU.
 5. The base station ofclaim 1, wherein the received data sequence comprises a packet-levelsequence number and the byte-level sequence number.
 6. The base stationof claim 1, further comprising a buffer configured to receive datasequences comprising a packet header and no user data part, said packetheader comprising a byte-level sequence number, which is set accordingto a virtual data associated with said data sequence.
 7. A method of abase station for content synchronization when broadcasting data in acommunications network, the method comprising: receiving data sequences(PDUs); wherein each received data sequence comprises byte-numberedsequence numbers; transmitting content of the received data sequences insynchronization with another base station using said byte-numberedsequence numbers; and determining if a PDU is lost.
 8. The method ofclaim 7, further comprising mapping said content to a correspondingradio resource block by relying on the byte-numbered sequence numbers.9. An arrangement for content synchronization when transmitting datafrom an infrastructure node in a communications network, saidarrangement comprising: processing circuitry configured to addbyte-numbered sequence numbers to a data sequence for transmission to abase station; and a transmitter configured to transmit the datasequences with byte-numbered sequence numbers and content to a pluralityof base stations, wherein said byte-numbered sequence numbers enablecontent synchronization by the base station and determining if a PDU islost.
 10. The arrangement of claim 9, wherein a SYNC protocol enablescontent synchronization by the base station.
 11. The arrangement ofclaim 9, wherein the arrangement is configured to obtain the sequencenumber of a subsequent packet by incrementing a sequence number of aprevious packet by a size of the previous packet.
 12. The arrangement ofclaim 9, wherein said arrangement is configured to add a packet-levelsequence number to said data sequences together with a byte-levelsequence number.
 13. A method of content synchronization whenbroadcasting data in a communications network, the method comprising:adding byte-numbered sequence numbers to content for transmission in adata sequence to a base station; and transmitting the data sequenceswith byte-numbered sequence numbers to a plurality of base stations;wherein said byte-numbered sequence numbers enable contentsynchronization by the base station and determining if a PDU is lost.14. The method of claim 13, further comprising mapping said content to acorresponding radio resource block by relying on the byte-numberedsequence numbers.
 15. The method of claim 13, further comprising:determining if a data sequence is lost and which data sequence or whichpart of said data sequence should be resumed upon transmission; andusing a sequence number of a subsequent received data sequence and asequence number of a last received data sequence to determine the lostnumber of bytes of data and determine transmission continuation withsubsequent data sequence.